The use of induction sealing of innerseal covers to containers is known in the art Typically, a round cover made from a metal foil is inductively sealed to a round container by placing a heat sealable material on one side of the cover and then placing the heat sealable material against the top of the container while the cover is subjected to induction heating. The induction heating heats the cover sufficiently to melt a heat sealable material such as a hot melt adhesive. When the hot melt adhesive cools, the cover adheres to the container. Unfortunately, once the cover is secured to the container, it is difficult for the consumer to remove the cover from a container. In order to make it easier for a consumer to remove the cover from the container, a tab is placed on the cover. The tab can be gasped between the thumb and forefinger so that it is easier for the user to peel the cover off of the container. The induction sealing of an irregular shaped cover with a tab or the like is difficult with a production line induction sealing unit because the elongated induction coils used in the production process to generate a magnetic field do not generate the induction heating in the proper regions of the irregular shaped cover. However, the elongated magnetic field is suitable for mass production of sealing units as it allows the cover and container to remain in the magnetic filed for an extended period of time to allow conduction of heat from one portion of a cover to other portions of the cover. That is, with regular round covers and round container the elongated induction coils are preferred in mass production as it allows the container and the cover to remain under the induction coil for a period of time while the heat generated by the current in the cover is transferred form one region of the cover to another region of the cover. This process works well for cylindrical covers and cylindrical containers; however using induction heating on a cover with an irregular shaped cover such as a cover with a tab one cannot uniformly heat the heat sealable materials on the cover with the elongated induction coils which results in a gap in the seal around the cover.
The present invention provides an apparatus and method for sealing a cover to a container where the shape of the container does not conform to the shape of either the cover or the magnetic field through the use of focusing members or flux concentrators that redirect the magnetic field to heat the cover in the region proximate the irregular shaped cover to thereby melt the heat sealable material so that one can form an airtight peripheral sealing relationship around a cover having a shape that is different from the shape of the container and different from the shape of the induction heating coil.